Various products containing the naturally-occurring mineral, gypsum, have been developed for the building trades. Especially notable are various gypsum wallboard products, e.g., sheet materials typically faced with material such as paper, non-woven glass fiber, or the like. In producing gypsum building products, calcined gypsum, i.e., anhydrous or hemihydrate (CaSO4.½H2O), known also as stucco, plaster of Paris, molding plaster, building plaster, and the like, typically in a slurry, is cast, molded, and dried. During the course of this process, the calcined gypsum is further hydrated, yielding hydrated gypsum (CaSO4.2H2O).
Gypsum building materials generally are held in high regard for use in fire-resistant construction. The spread of fire and the penetration of flame through set gypsum structures are delayed, because impinging heat initially operates to reverse the hydration reaction, recalcining gypsum, and liberating water. The liberated water is an additional energy sink, absorbing its heat of vaporization. Although gypsum doesn't burn, it shrinks and cracks when heated in a flame.
Although conventional gypsum may be fire resistant, gypsum with greater fire resistance properties and lower thermal conductivity is desirable.